The json file that describes your feature has the "last edit date" as a UTC timestamp (assuming AGOL). The time is the date/time of the last item added to the feature/table OR when its definition was last changed/updated.
"editingInfo" : {
"lastEditDate" : 1528926651042
},
If edit tracking is enabled, you can query the feature/table's "EditDate" field for the most recent update.